1. Field of the Invention
The present invention relates generally to thin dielectric films in magnetic head structures, and more particularly to the filling process of the read head gaps.
2. Description of the Related Art
Hard disk drives (HDD) are used in many modem devices, including computers, digital cameras, set-top-boxes for storing television programs, laser printers and GPS (global positioning system) devices. HDD""s usually consist of 1-22 disks covered with magnetic media and 1-44 magnetic heads. Recording heads, also known as magnetic heads, contain write and read elements. These elements are attached to a suspended slider. The preferred substrate material for the magnetic read heads is aluminum titanium carbide (AlTiC). Silicon, glass ceramics and fine-grained mixtures of Al2O3 and titanium carbide have also been evaluated by the magnetic head industry. Aluminum oxide is used for the insulation of the read element within a magnetic head.
The operating principle of modem magnetic heads is based on the magnetoresistive (MR) and giant magnetoresistive (GMR) effect. Area storage densities of 30-40 gigabits/square inch have been demonstrated, and the read element dimensions have been scaled down. The obtainable area recording density is affected by the track density and linear density. When the insulator layer thickness defining the magnetic head gap is reduced, the linear recording density increases. Gap layers of the read head are currently becoming thinner down to 30 nm. It is preferred that the gap layers have good dielectric strength, i.e., high breakdown voltages, and smooth surfaces without pinholes. As the area data storage density is further increased above 100 Gbits/square inch in the future, hard disk drive heads based on the laser-enhanced GMR, colossal magnetoresistive (CMR) or tunneling magnetoresistive (TMR) effect will possibly become commercially available. GMR heads are also used as magnetic sensors.
Highly integrated GMR heads have a significant thermal load during operation. As the temperature of the read head increases, the signal-to-noise ratio decreases, and the diffusion and electromigration rates increase, which are all undesirable effects. A good read element dissipates heat to the surroundings as efficiently as possible. Reducing the thickness of the insulator gap film improves the heat dissipation. Another possibility is to use dielectric material that has good heat conductivity. Aluminum oxide and aluminum nitride are examples of commercially available materials for the head gap fill. Mixtures of aluminum oxide and aluminum nitride are also feasible. RF magnetron sputtering has been used for thin film processing at low substrate temperatures. Plasma enhanced chemical vapor deposition (PECVD) has been another choice for the deposition of the dielectric material.
Desirable characteristics for the thin film material in a read head gap include the following:
High DC voltage breakdown (Vbd) value, e.g., Vbd greater than 6 MV/cm.
Low DC leakage current.
Low AC conductivity to enable high-frequency response of the magnetic head.
Continuous film, free of pinholes.
High step coverage, e.g.,  greater than 80-85%.
Good heat conductivity to dissipate the heat generated by the sensing current.
Low surface roughness Ra, e.g., Ra less than 1 nm.
Good corrosion resistance during magnetic head processing.
Low film thickness variation, e.g.,  less than 2% for a film thickness of 20 nm.
Good film adhesion.
Controllable residual stress.
Good mechanical strength against wear.
Good compatibility between the head gap fill material and the magnetic head materials, e.g., metals in a spin valve stack.
Exemplary materials in a giant magnetoresistive (GMR) read sensor and exemplary thicknesses include tantalum (Ta, typical layer thickness 3 nm), nickel-iron (NiFe, also known as permalloy, 4-6 nm), copper (Cu, 2-3 nm), cobalt (Co, 0.5 nm), cobalt-platinum-chromium (CoPtCr) and iron-manganese (FeMn). Magnetic shields can be made of NiFe-based materials. NiFe is a ferromagnetic layer that has xe2x80x9csoftxe2x80x9d magnetic behavior and serves as the sensing layer. Co has high spin-dependent electron scattering, and it increases the magnetoresistance ratio of the read sensor. Cu is a non-magnetic spacer layer that has a good match of its conduction band with the spin-up channel of the ferromagnetic layer. Other possible non-magnetic spacer materials are silver (Ag) and gold (Au). FeMn is an antiferromagnetic layer that pins the xe2x80x9chardxe2x80x9d (i.e., requiring very high magnetic fields to reorient) ferromagnetic layer CoPtCr. Other possible antiferromagnetic materials are terbium-cobalt (TbCo, which is actually a compensated ferrimagnet), and certain metal oxides, such as NiO, NiCoO and multilayered NiO/CoO. Ta is used as a seed layer at the bottom of the GMR stack (e.g., on a silicon surface) and as a cover layer on top of the FeMn layer. Examples of other possible seed layer materials are niobium (Nb), titanium (Ti) and zirconium (Zr). Thin film layer thicknesses in the spin valve are on the order of or smaller than the mean free path of the conduction electrons.
The magnetization of a bit on a magnetic medium (e.g., harddisk) affects the magnetic orientation of the sensing layer in the read head because the sensing layer has low coercive force. Low coercive force means that the magnetic orientation of the film can easily be flipped with a small external magnetic field, caused, e.g., by a magnetic bit on the magnetic medium. The pinned layer of the read head has high coercive force and it maintains its magnetic orientation in the magnetic field caused by a magnetic bit on the magnetic medium. A current is forced through the multilayer film stack. Depending on the magnetic orientation of the sensing layer, the read head has a different resistance. When the magnetic orientations of the sensing layer and the pinned layer are parallel, electron scattering in the read sensor is small and the read head has low resistance. When the magnetic orientations of the sensing layer and the pinned layer are antiparallel, electrons scatter a lot in the read sensor, and the read head has high resistance. Resistance changes are converted into voltage changes. When the magnetic orientations of the ferromagnetic sensing layer and pinned layer are forced to either parallel or antiparallel positions, the detection capability of the read head is at a maximum. There is a thin copper spacer to allow weak coupling between the two magnetic layers. The read head generally comprises an air-bearing surface.
Another type of magnetic read head is based on a tunneling structure. In a tunneling magnetoresistive (TMR) read head, two magnetic layers are separated by an insulating film, e.g., four molecular layers of Al2O3, to allow tunneling of electrons. This insulating layer is called a tunneling layer. The magnitude of tunneling current depends on the relative magnetic orientation of the hardened soft magnetic layers near the tunneling layer. When the magnetic orientations of the magnetic layers are antiparallel, the spins of the electrons do not match, and the tunneling structure has high resistance. When the magnetic orientations of the magnetic layers are parallel, the spins of the electrons match and the tunneling structure has low resistance.
The fabrication of magnetic heads has been described by R. Hsiao in IBM Journal of Research and Development, vol. 43, No. xc2xdxe2x80x94Plasma processing, xe2x80x9cFabrication of magnetic recording heads and dry etching of head materialsxe2x80x9d, which is incorporated by reference herein.
Kotaro Yamamoto has described the manufacturing of spin-valve read heads in U.S. Pat. No. 6,128,160, priority date Jun. 30, 1997 and issued Oct. 3, 2000. In this patent, sputtering is used for the deposition of thin films. There are two insulator layers made of sputtered Al2O3.
The disadvantage of K. Yamamoto""s method is that sputtering tends to produce pinholes in the Al2O3 film, thus lowering the breakdown voltage of the insulator. Another disadvantage of this method is that the step coverage of a sputtered Al2O3 layer on an uneven surface is far below 100%.
Masamichi Saito et al. have described a magnetoresistive sensor and head in U.S. Pat. No. 6,153,062 (xe2x80x9cthe ""062 patentxe2x80x9d), priority date Sep. 7, 1997 and issued Nov. 28, 2000. DC magnetron sputtering and RF sputtering were used for the deposition of the thin films. FIG. 1 of the ""062 patent illustrates a dual sensor structure. There is a silicon substrate 2. A first shielding layer 4 having high permeability, e.g., NiFe alloy, is deposited on the substrate. A first gap insulator layer 6 consisting of about 30 nm of Al2O3 is deposited on the NiFe surface. A seed layer 8 (3 nm Ta) is deposited over the Al2O3. Then the spin valve is formed over the seed layer 8, including a free magnetic layer 10 (4 nm NiFe), a non-magnetic conductive layer 12 (2.5 nm Cu), a pinned layer 14 (4 nm NiFe), an antiferromagnetic layer 16 (20 nm PtMn alloy), another pinned layer 18 (4 nm NiFe), another non-magnetic conductive layer 20 (2.5 nm Cu) and another free magnetic layer 22 (4 nm NiFe). Finally a top layer 24 (3 nm Ta) is deposited. The structure is masked, patterned and etched. Then the deposition is continued with hard bias layers 26 (30 nm CoPt alloy) and electrically conductive layers 28 (W or Cu). The role of the hard bias layer is to prevent the formation of a plurality of magnetic domains in the sensing layer. A second gap insulator layer 30 (30 nm Al2O3) is deposited on a surface that consists of Ta and W or Cu surfaces. A second shield layer 32 (e.g., NiFe alloy) is deposited on the second head gap layer 30. The magnetic gap length is determined by the distance between the first and the second shield layers. The magnetic gap length can be decreased if the first and the second head gap insulator layers 6 and 30 can be made thinner.
The method in U.S. Pat. No. 6,153,062 disadvantageously results in pinholes in the Al2O3 film that lower the breakdown voltage of the insulator and in poor step coverage of Al2O3 on the uneven surface.
A structure and method of fabricating a magnetic read head, comprising forming a fill layer for a magnetic read head gap using atomic layer deposition (ALD), is disclosed. The fill layer comprises an insulator, preferably aluminum oxide, aluminum nitride, mixtures thereof and layered structures thereof. The thickness of the ALD-formed head gap fill layer preferably is between approximately 5 nm and 100 nm, more preferably between approximately 10 nm and 40 nm.
Alternatively, the gap fill material comprises an ALD-formed layered structure of aluminum oxide and a compound with high thermal conductivity, such as beryllium oxide or boron nitride.
The magnetic read head comprises a magnetic sensing element such as a GMR (giant magnetoresistive), CMR (colossal magnetoresistive) or TMR (tunneling magnetoresistive) sensor.